UGT1A1*6 (211G>A), UGT1A1*28 (TA6>TA7), UGT1A1*60 (−3279T>G), UGT1A7 (387T>G), UGT1A7 (622T>C), and UGT1A9*1b (−118T9>T10, also named *22) were genotyped in 123 patients with metastatic colorectal cancer who had received irinotecan-based chemotherapy. Here, UGT1A1 is linked to metastatic colorectal cancer.